As an image recording method for recording an image on a recording medium such as a paper based on an image data signal, a variety of recording methods such as an electrophotographic method, a thermal transfer method, and an inkjet method are known. In particular, the inkjet method has the advantage that running cost is low and noise is low since an image can be printed by an inexpensive apparatus and the image is directly printed by ejecting an ink to an area where ink deposition is required.
In a recording method utilizing an inkjet method, recording can be performed not only on a paper medium such as a plain paper but on a non-water-absorptive recording medium such as a plastic film or a metal plate. However, since an ink is not absorbed when applied to a non-water-absorptive recording medium, it is difficult to speed up recording and to provide a high quality image, and further, adhesion of the printed image to the recording medium tends to be insufficient.
One example of recording methods utilizing an inkjet method is a recording method using an ink which is curable by irradiation of a radiation. In this method, an ink is ejected and then irradiated with a radiation to cure an ink droplet, whereby a recording speed can be improved and an image having higher sharpness and enhanced adhesion can be formed.
In this method, it is expected that the recording speed and adhesion can be further improved by increasing the sensitivity of the ink for inkjet recording which is curable by irradiation of a radiation such as an ultraviolet ray, and by improving the curability. It is thought that increasing the sensitivity also contributes to improvement of the strength of a printed image.
As a technique related to the above, an inkjet ink composition including a dendritic amide polymer compound having a branched structure, a polymerization initiator, and a radically polymerizable compound is disclosed. It is reported that this inkjet ink composition is excellent in adhesion of an ink image film to a substrate, film strength, and ejection stability (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2013-082916).
As another technique, an ink composition is disclosed, the ink composition including a polymer including a thiol group and, on a side chain, a partial structure selected from the group consisting of a fluorine-substituted hydrocarbon group, a siloxane skeleton, and a long chain alkyl group, a photopolymerization initiator, and a polymerizable compound (see, for example, JP-A No. 2010-001437). It is thought that, in this ink composition, the polymer including a thiol group and a partial structure having a surface orientation localizes in the surface of the ink composition and increases crosslinking density, and, therefore, the ink composition has a favorable curing sensitivity and has, for example, excellent scratch resistance and excellent anti-blocking properties.